Summary: Synapsin, N-terminal domain
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Synapsin Edit Wikipedia article
|Synapsin, N-terminal domain|
Structure of the c domain of synapsin IA from bovine brain.
|Synapsin, ATP binding domain|
The synapsins are a family of proteins that have long been implicated in the regulation of neurotransmitter release at synapses. Specifically, they are thought to be involved in regulating the number of synaptic vesicles available for release via exocytosis at any one time.Synapsins are present in invertebrates and vertebrates and are somewhat homologous across evaluated vertebrates.
Current studies suggest the following hypothesis for the role of synapsin: synapsins bind synaptic vesicles to components of the cytoskeleton which prevents them from migrating to the presynaptic membrane and releasing transmitter. During an action potential, synapsins are phosphorylated by PKA (cAMP dependent protein kinase), releasing the synaptic vesicles and allowing them to move to the membrane and release their neurotransmitter.
Gene knockout studies in mice (where the mouse is unable to produce synapsin) have had some surprising results. Mice lacking all three synapsins are prone to seizures, and experience learning defects. These results suggest that while synapsins are not essential for synaptic function, they do serve an important modulatory role. Conversely, studies using transgenic mice in which neuronal signaling is abolished in specific circuitries showed that synaptic activity regulates, but is not essential to maintain, the expression of these proteins.
Humans and most other vertebrates possess three genes encoding three different synapsin proteins. Each gene in turn is alternatively spliced to produce at least two different protein isoforms for a total of six isoforms:
|SYN1||Synapsin I||Ia, Ib|
|SYN2||Synapsin II||IIa, IIb|
|SYN3||Synapsin III||IIIa, IIIb|
Different neuron terminals will express varying amounts of each of these synapsin proteins and collectively these synapsins will comprise 1% of the total expressed protein at any one time. Synapsin Ia has been implicated in bipolar disorder and schizophrenia.
- Esser L, Wang CR, Hosaka M, Smagula CS, Südhof TC, Deisenhofer J (February 1998). "Synapsin I is structurally similar to ATP-utilizing enzymes". EMBO J. 17 (4): 977–84. doi:10.1093/emboj/17.4.977. PMC 1170447. PMID 9463376.
- Evergren E, Benfenati F, Shupliakov O (September 2007). "The synapsin cycle: a view from the synaptic endocytic zone". J. Neurosci. Res. 85 (12): 2648–56. doi:10.1002/jnr.21176. PMID 17455288.
- Rosahl TW, Geppert M, Spillane D, Herz J, Hammer RE, Malenka RC, Sudhof TC (1993). "Short-term synaptic plasticity is altered in mice lacking synapsin I". Cell 75 (4): 661–670. doi:10.1016/0092-8674(93)90487-B. PMID 7902212.
- Kihara AH, Santos TO, Paschon V, Matos RJ, Britto LR (2008). "Lack of photoreceptor signaling alters the expression of specific synaptic proteins in the retina". Neuroscience 151 (4): 995–1005. doi:10.1016/j.neuroscience.2007.09.088. PMID 18248909.
- Kao HT, Porton B, Hilfiker S, Stefani G, Pieribone VA, DeSalle R, Greengard P (December 1999). "Molecular evolution of the synapsin gene family". J. Exp. Zool. 285 (4): 360–77. doi:10.1002/(SICI)1097-010X(19991215)285:4<360::AID-JEZ4>3.0.CO;2-3. PMID 10578110.
- Gitler D, Xu Y, Kao HT, Lin D, Lim S, Feng J, Greengard P, Augustine GJ (April 2004). "Molecular determinants of synapsin targeting to presynaptic terminals". J. Neurosci. 24 (14): 3711–20. doi:10.1523/JNEUROSCI.5225-03.2004. PMID 15071120.
- Ferreira A, Rapoport M (April 2002). "The synapsins: beyond the regulation of neurotransmitter release". Cell. Mol. Life Sci. 59 (4): 589–95. doi:10.1007/s00018-002-8451-5. PMID 12022468.
- Vawter, MP et al (April 2002). "Reduction of synapsin in the hippocampus of patients with bipolar disorder and schizophrenia". Mol. Psychiatry 7 (6): 571–8. doi:10.1038/sj.mp.4001158. PMID 12140780.
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External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR020897
The synapsins are a family of neuron-specific phosphoproteins that coat synaptic vesicles and are involved in the binding between these vesicles and the cytoskeleton (including actin filaments). The family comprises 5 homologous proteins Ia, Ib, IIa, IIb and III. Synapsins I, II, and III are encoded by 3 different genes. The a and b isoforms of synapsin I and II are splice variants of the primary transcripts [PUBMED:10940454].
Synapsin I is mainly associated with regulation of neurotransmitter release from presynaptic neuron terminals [PUBMED:2859595]. Synapsin II, as well as being involved in neurotransmitter release, has a role in the synaptogenesis and synaptic plasticity responsible for long term potentiation [PUBMED:7777057]. Recent studies implicate synapsin III with a developmental role in neurite elongation and synapse formation that is distinct from the functions of synapsins I and II [PUBMED:10804215].
Structurally, synapsins are multidomain proteins, of which 3 domains are common to all the mammalian forms. The N-terminal `A' domain is ~30 residues long and contains a serine residue that serves as an acceptor site for protein kinase-mediated phosphorylation. This is followed by the `B' linker domain, which is ~80 residues long and is relatively poorly conserved. Domain `C' is the longest, spanning approximately 300 residues. This domain is highly conserved across all the synapsins (including those from Drosophila) and is possessed by all splice variants. The remaining six domains, D-I, are not shared by all the synapsins and differ both between the primary transcripts and the splice variants.
This entry represents the pre-ATP-grasp structural domain found in synapsins, which precedes the ATP-grasp domain. The structure of the pre-ATP-grasp domain consists of alpha/beta/alpha in three layers, and is possibly a rudiment form of the Rossmann-fold. This domain can have a substrate-binding function.
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Cellular component||synaptic vesicle (GO:0008021)|
|Biological process||neurotransmitter secretion (GO:0007269)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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|Previous IDs:||Synapsin; Synapsin_N;|
|Author:||Mian N, Bateman A, Griffiths-Jones SR|
|Number in seed:||4|
|Number in full:||232|
|Average length of the domain:||96.20 aa|
|Average identity of full alignment:||58 %|
|Average coverage of the sequence by the domain:||19.27 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||11|
|Download:||download the raw HMM for this family|
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Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
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Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
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There are 2 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Synapsin domain has been found. There are 20 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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